The Crayfish Preface

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The Crayfish: An Introduction to the Study of Zoology T. H. Huxley

(sel) (1879)

Preface

[v] In writing this book about Crayfishes it has not been my intention to compose a zoologicalmonograph on that group of animals. Such a work, to be worthy of the name, would require thedevotion of years of patient study to a mass of materials collected from many parts of the worlds.

Nor has it been my ambition to write a treatise upon our English crayfish, which should in anyway provoke comparison with the memorable labours of Lyonet, Bojanus, or Strauss Durckheim,upon the willow caterpillar, the tortoise, and the cockehafer. What I have had in view is a muchhumbler, though perhaps, in the present state of science, not less useful object. I have desired, infact, to show how the careful study of one of the commonest and most insignificant of animals,leads us, step by step, from every-day knowledge to the widest generalizations [vi] and the mostdifficult problems of zoology; and, indeed, of biological science in general.

It is for this reason that I have termed the book an "Introduction to Zoology." For, whoever willfollow its pages, crayfish in hand, and will try to verify for himself the statements which itcontains, will find himself brought face to face with all the great zoological questions whichexcite so lively an interest at the present day; he will understand the method by which alone wecan hope to attain to satisfactory answers of these questions; and, finally, he will appreciate the

justice of Diderot's remark, 'It faut être profond dans l'art ou dans la science pour en bien posséder les éléments."



And these benefits will accrue to the student whatever shortcomings and errors in the work itself may be made apparent by the process of verification. 'Common and lowly as most may think thecray-fish," well says Roesel von Rosenhof, "it is yet so full of wonders that the greatest naturalistmay be puzzled to give a clear account of it." But only [vii] the broad facts of the case are of fundamental importance; and, so far as these are concerned, I venture to hope that no error has

slipped into my statement of them. As for the details, it must be remembered, not only that someomission or mistake is almost unavoidable, but that new lights come with new methods of investigation and that better modes of statement follow upon the improvement of our generalviews introduced by the gradual widening of our knowledge.

I sincerely hope that such amplifications and rectifications may speedily abound; and that thissketch may be the means of directing the attention of observers in all parts of the world to thecrayfishes. Combined efforts will soon furnish the answers to many questions which a singleworker can merely state; and, by completing the history of one group of animals, secure thefoundation of the whole of biological science.

In the Appendix, I have added a few notes respecting points of detail with which I thought it[viii] unnecessary to burden the text; and, under the head of Bibliography, I have given somereferences to the literature of the subject which may be useful to those who wish to follow it outmore fully.

I am indebted to Mr. T. J. Parker, demonstrator of my biological class, for several anatomicaldrawings; and for valuable aid in supervising the execution of the woodcuts, and in seeing thework through the press.

Mr. Cooper has had charge of the illustrations, and I am indebted to him and to Mr. Coombs, theaccurate and skilful draughtsman to whom the more difficult subjects were entrusted, for such

excellent specimens of xylographic art as the figures of the Crab, Lobster, Rock Lobster, and Norway Lobster.

From Chapter I. The Natural History of the Common Crayfish ( Astacus fluviatilis. )

[1] Many persons seem to believe that what is termed Science is of a widely different naturefrom ordinary knowledge, and that the methods by which scientific truths are ascertained involvemental operations of a recondite and mysterious nature, comprehensible only by the initiated,and as distinct in their character as in their subject matter, from the processes by which wediscriminate between fact and fancy in ordinary life.

But any one who looks into the matter attentively will soon perceive that there is no solidfoundation for the belief that the realm of science is thus shut off from that of common sense; or that the mode of investigation which yields such wonderful results to the scientific investigator,is different in kind from that which is employed [2] for the commonest purposes of everydayexistence. Common sense is science exactly in so far as it fulfils the ideal of common sense; thatis, sees facts as they are, or, at any rate, without the distortion of prejudice, and reasons fromthem in accordance with the dictates of sound judgment. And science is simply common sense atits best; that is, rigidly accurate in observation, and merciless to fallacy in logic.



Whoso will question the validity of the conclusions of sound science, must be prepared to carryhis scepticism a long way; for it may be safely affirmed, that there is hardly any of thosedecisions of common sense on which men stake their all in practical life, which can justify itself so thoroughly on common sense principles, as the broad truths of science can be justified.

The conclusion drawn from due consideration of the nature of the case is verified by historicalinquiry; and the historian of every science traces back its roots to the primary stock of commoninformation possessed by all mankind.

In its earliest development knowledge is self-sown. Impressions force themselves upon men'ssenses whether they will or not, and often against their will. The amount of interest which theseimpressions awaken is determined by the coarser pains and pleasures which they carry in their train, or by mere curiosity; and reason deals with the materials supplied to it as far as that interestcarries it, and no farther. Such common [3] knowledge is rather brought than sought; and suchratiocination is little more than the working of a blind intellectual instinct.

It is only when the mind passes beyond this condition that it begins to evolve science. Whensimple curiosity passes into the love of knowledge as such, and the gratification of the aestheticsense of the beauty of completeness and accuracy seems more desirable than the easy indolenceof ignorance; when the finding out of the causes of things becomes a source of joy, and he iscounted happy who is successful in the search; common knowledge of nature passes into whatour forefathers called Natural History, from whence there is but a step to that which used to betermed Natural Philosophy, and now passes by the name of Physical Science.

In this final stage of knowledge, the phenomena of nature are regarded as one continuous seriesof causes and effects; and the ultimate object of science is to trace out that series, from the termwhich is nearest to us, to that which is at the furthest limit accessible to our means of

investigation.The course of nature as it is, as it has been, and as it will be, is the object of scientific inquiry;whatever lies beyond, above, or below this, is outside science. But the philosopher need notdespair at the limitation of his field of labour: in relation to the human mind Nature is boundless;and, though nowhere inaccessible, she is everywhere unfathomable.

[4] The Biological Sciences embody the great multitude of truths which have been ascertainedrespecting living beings; and as there are two chief kinds of living things, animals and plants, soBiology is, for convenience sake, divided into two main branches, Zoology and Botany.

Each of these branches of Biology has passed through the three stages of development, which arecommon to all the sciences; and, at the present time, each is in these different stages in differentminds. Every country boy possesses more or less information respecting the plants and animalswhich come under his notice, in the stage of common knowledge; a good many persons haveacquired more or less of that accurate, but necessarily incomplete and unmethodised knowledge,which is understood by Natural History; while a few have reached the purely scientific stage,and, as Zoologists and Botanists, strive towards the perfection of Biology as a branch of PhysicalScience.



Historically, common knowledge is represented by the allusions to animals and plants in ancientliterature; while Natural History, more or less grading into Biology, meets us in the works of Aristotle, and his continuators in the Middle Ages, Rondoletius, Aldrovandus, and their contemporaries and successors. But the conscious attempt to construct a complete science of Biology hardly dates further back than Treviranus and Lamarck, at the beginning of this century,

while it has received its strongest impulse, in our own day, from Darwin.

[5] My purpose, in the present work, is to exemplify the general truths respecting thedevelopment of zoological science which have just been stated by the study of a special case;and, to this end, I have selected an animal, the Common Crayfish, which, taking it altogether, is

better fitted for my purpose than any other.

It is readily obtained ,1 and all the most important points of its construction are easily deciphered;hence, those who read what follows will have no difficulty in ascertaining whether thestatements correspond with facts or not. And unless my readers are prepared to take this muchtrouble, they may almost as well shut the book; for nothing is truer than Harvey's dictum, that

those who read without acquiring distinct images of the things about which they read, by the helpof their own senses, gather no real knowledge, but conceive mere phantoms and idols.

It is a matter of common information that a number of our streams and rivulets harbour smallanimals, rarely more than three or four inches long, which are very similar to little lobsters,except that they are usually of a dull, greenish or brownish colour, generally diversified with paleyellow on the under side of the body, and sometimes with red on the limbs. In rare cases, their [6] general hue may be red or blue. These are "crayfishes," and they cannot possibly be mistakenfor any other inhabitants of our fresh waters.

Fig. 1. – Astacus fluviatilis – Side view of a male specimen (nat. size): – bg, branchiostegite; cg, cervical groove; r, rostrum; t, telson. – 1, eye-stalk; 2, antennule; 3,antenna; 9, external maxillipede; 10, forceps; 14, last ambulatory leg; 17, third abdominalappendage; 20, lateral lobe of the tail-fin, or sixth abdominal appendage; xv, the first; and xx, thelast abdominal somite. In this and in succeeding figures the numbers of the somites are given inRoman, those of the appendages in ordinary numerals.

The animals may be seen walking along the bottom of the shallow waters which they prefer, bymeans of four pairs of jointed legs (fig. 1); but, if alarmed, they swim [7] backwards with rapid

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jerks, propelled by the strokes of a broad, fan-shaped flipper, which terminates the hinder end of the body (fig. 1, t, 20). In front of the four pairs of legs, which are used in walking, there is a pair of limbs of a much more massive character, each of which ends in two claws disposed in such amanner as to constitute a powerful pincer (fig. 1; 10). These claws are the chief weapons of offence and defence of the crayfish, and those who handle them incautiously will discover that

their grip is by no means to be despised, and indicates a good deal of disposable energy. A sortof shield covers the front part of the body, and ends in a sharp projecting spine in the middle line(r ). On each side of this is an eye, mounted on a movable stalk ( 1), which can be turned in anydirection: behind the eyes follow two pairs of feelers; in one of these, the feeler ends in two,short, jointed filaments ( 2); while, in the other, it terminates in a single, many-jointed filament,like a whip-lash, which is more than half the length of the body ( 3). Sometimes turned

backwards, sometimes sweeping forwards, these long feelers continually explore a considerablearea around the body of the crayfish.

If a number of crayfishes, of about the same size, are compared together, it will easily be seenthat they fall into two sets; the jointed tail being much: broader, especially in the middle, in the

one set than in the other (fig. 2). The broad-tailed crayfishes are the [8] females, the others themales. And the latter may be still more easily known by the possession of four curved styles,attached to the under face of the first two rings of the tail, which are turned forwards between thehinder legs, on the under side of the body (fig. 3, A; 15, 16 ). In the female, there are mere softfilaments in the place of the first pair of styles (fig. 8, B; 15).

Crayfishes do not inhabit every British river, and even where they are known to abound, it is noteasy to find them at all times of the year. In granite districts and others, in which the soil yieldslittle or no calcareous matter to the waters which flow over it, crayfishes do not occur. They areintolerant of great heat and of much sunshine; they are therefore most active towards theevening, while they shelter themselves under the shade of stones and banks during the day. It has

been observed that they frequent those parts of a river which run north and south, less than thosewhich have an easterly and westerly direction, inasmuch as the latter yield more shade from themidday sun.

During the depth of winter, crayfishes are rarely to be seen about in a stream; but they may befound in abundance in its banks, in natural crevices and in burrows which they dig for themselves. The burrows may be from a few inches to more than a yard deep, and it has beennoticed that, if the waters are liable to freeze, the burrows are deeper and further from the surfacethan otherwise. Where the soil, through [9] which a stream haunted by crayfishes runs, is softand peaty, the crayfishes work their way into it in all directions, and thousands of them, of allsizes, may be dug out, even at a considerable distance from the banks.

It does not appear that crayfishes fall into a state of torpor in the winter, and thus "hybernate" inthe strict sense of the word. At any rate, so long as the weather is open, the crayfish lies at themouth of his burrow, barring the entrance with his great claws, and with protruded feelers keepscareful watch on the passersby. Larvæ of insects, water-snails, tadpoles, or frogs, which comewithin reach, are suddenly seized and devoured, and it is averred that the water-rat is liable to thesame fate. Passing too near the fatal den, possibly in search of a stray crayfish, whose flavour he



highly appreciates, the vole is himself seized and held till he is suffocated, when his captor easilyreverses the conditions of the anticipated meal.

In fact, few things in the way of food are amiss to the crayfish; living or dead, fresh or carrion,animal or vegetable, it is all one. Calcareous plants, such as the stoneworts ( Chara ), are highly

acceptable; so are any kinds of succulent roots, such as carrots; and it is said that crayfishsometimes make short excursions inland, in search of vegetable food. Snails are devoured, shellsand all; the cast coats of other crayfish are turned to account as supplies of needful calcareousmatter; and the unprotected or weakly member of the family is [10] not spared. Crayfishes, infact, are guilty of cannibalism in its worst form; and a French observer pathetically remarks, that,under certain circumstances, the males "méconnaissent les plus saints devoirs ; " and, not contentwith mutilating or killing their spouses, after the fashion of animals of higher moral pretensions,they descend to the lowest depths of utilitarian turpitude, and finish by eating them.

In the depth of winter, however, the most alert of crayfish can find little enough food; and hence,when they emerge from their hiding-places in the first warm days of spring, usually about

March, the crayfishes are in poor condition.

At this time, the females are found to be laden with eggs, of which from one to two hundred areattached beneath the tail, and look like a mass of minute berries (fig. 3, B). In May or June, theseeggs are hatched, and give rise to minute young, which are sometimes to be found attached

beneath the tail of the mother, under whose protection they spend the first few days of their existence.

In this country, we do not set much store upon crayfishes as an article of food, but on theContinent, and especially in France, they are in great request. Paris alone, with its two millions of inhabitants, consumes annually from five to six millions of crayfishes, and pays about £16,000

for them. The natural productivity of the rivers of France has long been inadequate to supply the[11] demand for these delicacies; and hence, not only are large quantities imported fromGermany, and elsewhere, but the artificial cultivation of crayfish has been successfully attemptedon a considerable scale.

Crayfishes are caught in various ways; sometimes the fisherman simply wades in the water anddrags them out of their burrows; more commonly, hoop-nets baited with frogs are let down intothe water and rapidly drawn up, when there is reason to think that crayfish have been attracted tothe bait; or fires are lighted on the banks at night, and the crayfish, which are attracted, likemoths, to the unwonted illumination, are scooped out with the hand or with nets.

Thus far, our information respecting the crayfish is such as would be forced upon anyone whodealt in crayfishes, or lived in a district in which they were commonly used for food. It iscommon knowledge. Let us now try to push our acquaintance with what is to be learned aboutthe animal a little further, so as to be able to give an account of its Natural History, such as mighthave been furnished by Buffon if he had dealt with the subject.

There is an inquiry which does not strictly lie within the province of physical science, and yetsuggests itself naturally enough at the outset of a natural history.



such an objector to open a conversation about his own business with a carpenter, or an engineer,or, still better, with a sailor, and try how far plain English will go. The interview will not havelasted long before he will find himself lost in a maze of unintelligible technicalities. Everycalling has its technical terminology; and every artisan uses terms of art, which sound likegibberish to those who know nothing of the art, but are exceedingly convenient to those who

practise it.

In fact, every art is full of conceptions which are special to itself; and, as the use of language is toconvey our conceptions to one another, language must supply signs for those conceptions. Thereare two ways of doing this: either existing signs may be combined in loose and cumbrous

periphrases; or new signs, having a well-understood and definite signification, may be invented.The practice of sensible people shows the advantage of the latter course; and here, as elsewhere,science has simply followed and improved upon common sense.

[15] Moreover, while English, French, German, and Italian artisans are under no particular necessity to discuss the processes and results of their business with one another, science is

cosmopolitan, and the difficulties of the study of Zoology would be prodigiously increased, if Zoologists of different nationalities used different technical terms for the same thing. They needa universal language; and it has been found convenient that the language shall be the Latin inform, and Latin or Greek in origin. What in English is Crayfish, is Ecrevisse inFrench; Flusskrebs, in German; Cammaro, or Gambaro, or Gammarello, in Italian: but theZoologist of each nationality knows that, in the scientific works of all the rest, he shall find whathe wants to read under the head of Astacus fluviatilis.

But granting the expediency of a technical name for the Crayfish, why should that name bedouble? The reply is still, practical convenience. If there are ten children of one family, we donot call them all Smith, because such a procedure would not help us to distinguish one from the

other; nor do we call them simply John, James, Peter, William, and so on, for that would not helpus to identify them as of one family. So we give them all two names, one indicating their closerelation, and the other their separate individuality – as John Smith, James Smith, Peter Smith,William Smith, & c. The same thing is done in Zoology; only, in accordance with the genius of the Latin language, [16] we put the Christian name, so to speak, after the surname.

There are a number of kinds of Crayfish, so similar to one another that they bear the commonsurname of Astacus. One kind, by way of distinction, is called fluviatile, another slender-handed, another Dauric, from the region in which it lives; and these double names are rendered

by – Astacus fluviatilis, Astacus leptodactylus, and Astacus dauricus ; and thus we have anomenclature which is exceedingly simple in principle, and free from confusion in practice. AndI may add that, the less attention is paid to the original meaning of the substantive and adjectiveterms of this binomial nomenclature, and the sooner they are used as proper names, the better.Very good reasons for using a term may exist when it is first invented, which lose their validitywith the progress of knowledge. Thus Astacus fluviatilis was a significant name so long as weknew of only one kind of crayfish; but now that we are acquainted with a number of kinds, all of which inhabit rivers, it is meaningless. Nevertheless, as changing it would involve endlessconfusion, and the object of nomenclature is simply to have a definite name for a definite thing,nobody dreams of proposing to alter it.



Having learned this much about the origin of the names of the crayfish, we may next proceed toconsider those points which an observant Naturalist, who did not [17] care to go far beyond thesurface of things, would find to notice in the animal itself.

Probably the most conspicuous peculiarity of the crayfish, to any one who is familiar only with

the higher animals, is the fact that the hard parts of the body are outside and the soft parts inside;whereas in ourselves, and in the ordinary domestic animals, the hard parts, or bones, whichconstitute the skeleton, are inside, and the soft parts clothe them. Hence, while our hardframework is said to be an endoskeleton, or internal skeleton; that of the crayfish is termedan exoskeleton, or external skeleton. It is from the circumstance that the body of the crayfishes isenveloped in this hard crust, that the name of Crustacea is applied to them, along with the crabs,shrimps, and other such animals. Insects, spiders, and centipedes have also a hard exoskeleton,

but it is usually not so hard and thick as in the Crustacea.

If a piece of the crayfish's skeleton is placed in strong vinegar, abundant bubbles of carbonic acidgas are given off from it, and it rapidly becomes converted into a soft laminated membrane,

while the solution will be found to contain lime. In fact the exoskeleton is composed of a peculiar animal matter, so much impregnated with carbonate and phosphate of lime that it becomes dense and hard.

It will be observed that the body of the crayfish is naturally marked out into several distinctregions. There

Fig. 2. – Astacus fluviatilis. – Dorsal or tergal view (nat. size). A, male; B. female: – bcg, branchio-cardiac groove, which marks the boundary between the periocardial and the bronchialcavities; cg, cervical groove; these letters are placed on the carapace; r, rostrum; t, t', the twodivisions of the telson; 1, eye-stalks; 2, antennules; 3, antennæ); 20, lateral lobes of tail-fin; xv-xx, somites of the abdomen.



[19] is a firm and solid front part, covered by a large continuous shield, which is calledthe carapace; and a jointed hind part, commonly termed the tail (fig. 2). From the perception of a

partially real, and partially fanciful, analogy with the regions into which the body is divided inthe higher animals, the fore part is termed the cephalo-thorax, or head ( cephalon ) and chest(thorax ) combined, while the hinder part receives the name of abdomen. . . .

[328] Many of these fluviatile prawns differ from the marine species not only in their great size(some attaining a foot or more in length), but still more remarkably in the vast development of the fifth pair of thoracic appendages. These are always larger than the slender fourth pair (whichanswer to the forceps of the crayfishes); and, in the males especially, they are very long andstrong, and [329] are terminated by great chelae, not unlike those of the crayfishes. Hence thesefluviatile prawns (known in many places by the name of "Cammarons") are not unfrequentlyconfounded with true crayfishes; though the fact that there are only three pair of ordinary legs

behind the largest, forceps-like pair, is sufficient at once to distinguish them from any of the Astacidae.

Species of these large-clawed prawns live in the [330] brackish water lagoons of the Gulf of Mexico, but I am not aware that any of them have yet been met with in the sea itself. ThePalaemon lacustris (Anchistia migratoria, Heller) abounds in fresh-water ditches and canals

between Padua and Venice, and in the Lago di Garda, as well as in the brooks of Dalmatia; butits occurrence in the Adriatic or the Mediterranean, which has been asserted, appears to bedoubtful. So the Nile prawn,

though very similar to some Mediterranean prawns, does not seem to be identical with any at present known. . . .

[337] The hypothesis respecting the origin of crayfishes [338] which has been tentatively put

forward in the preceding pages, involves the assumption that marine Crustace of the astacinetype were in existence during the deposition of the mobile tertiary formations, when the greatcontinents began to assume their present shape. That such was the case there can be no doubt,inasmuch as abundant remains of Crustacea of that type occur still earlier in the mesozoic rocks.They prove the existence of ancient crustaceans, from which the crayfishes may have beenderived, at that period of the earth’s history when the conformation of the land and sea were suchas to admit of their entering the regions in which we now find them.



The materials which have, up to the present time, been collected are too scanty to permit of thetracing out of all the details of the geneology of the crayfish. Nevertheless, the evidence whichexists is perfectly clear, as far as it goes, and is in complete accordance with the requirements of the doctrine of evolution. . . .

[346] Thus, with respect to the Aetiology of the crayfishes, all the known facts are in harmonywith the requirements of the hypothesis that they have been gradually evolved in the course of the Mesozoic and subsequent epochs of the world’s history from a primitive Astacomorphousform.

And it is well to reflect that the only alternative supposition is, that these numerous successiveand coexistent forms of insignificant animals, the differences of which require careful study for their discrimination, have been separately and independently fabricated, and put into thelocalities in which we find them. By whatever verbal fog the question at issue may be hidden,this is the real nature of the dilemma presented to us not only by the crayfish, but by everyanimal and every plant; from man to the humblest animacule; from the spreading beech and

towering pine to the Micrococci which lie at the limit of microscopic visibility.

1 If crayfish are not to be had, a lobster will be found to answer to the description of the former,in almost all points; but the gills and the abdominal appendages present differences; and the lastthoracic somite is united with the rest in the lobster. (See Chap. V.)

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